Aim. The aim of this investigation is to reduce blood transfusion in cardiac surgery patients with preoperative conditions predictive for transfusion requirements. We compared the amount of blood transfused in two groups of patients undergoing cardiopulmonary bypass (CPB) with two different circuit systems.Methods. Sixty patients undergoing cardiac surgery were randomly assigned to two groups: in group A (N=30) cardiopulmonary bypass was accomplished with an open circuit and in group B (N=30) with a closed circuit. The open circuit consisted of a cardiotomy reservoir, a membrane oxygenator and an arterial line filter, while the closed circuit was made up of a collapsible venous reservoir, a membrane oxygenator, an arterial line filter and a cardiotomy reservoir. The amount of transfused packed red cells in each patient was measured until discharge from the hospital.Results. Groups were similar regarding age, gender, body surface area (BSA), New York Heart Association (NYHA) class and comorbidity risk factors. Moreover, there were no significant differences between groups regarding the type of procedures, CPB and aortic cross-clamp times, total amount of cardioplegia and urinary output during CPB. Priming volume was 1180±84 mL (group A) and 760±72 mL (group B) (P<0.001). Significant differences in transfusion requirements emerged in the two groups: the total volume of packed red cells transfused for each patient was significantly higher in the open system group compared to the closed system group (717±486 mL versus 378±364 mL) (P=0.003). Clinical outcomes were similar in both groups.Conclusion. In patients with preoperative conditions predictive for the need of transfusions, the use of a closed cardiopulmonary bypass circuit can diminish the amount of transfused blood products.